Fuel rails for supplying fuel to fuel injectors of internal combustion engines are well known. A fuel rail assembly, also referred to herein simply as a fuel rail, is essentially an elongate fuel manifold connected at an inlet end to a fuel supply system and having a plurality of ports for mating in any of various arrangements with a plurality of fuel injectors to be supplied. Typically, a fuel rail assembly includes a plurality of fuel injector sockets in communication with a manifold supply tube, the injectors being inserted into the sockets and held in place in an engine head by bolts securing the fuel rail assembly to the head.
Gasoline fuel injection arrangements may be divided generally into multi-port fuel injection (MPFI), wherein fuel is injected into a runner of an air intake manifold ahead of a cylinder intake valve, and direct injection (DIG), wherein fuel is injected directly into an engine cylinder, typically during or at the end of the compression stroke of the piston. Diesel fuel injection is also a direct injection type.
For purposes of clarity and brevity, wherever DIG is used herein it should be taken to mean both DIG and DID, and fuel cell rail assemblies in accordance with the invention as described below are useful in both DIG and DID engines.
DIG fuel rails require high precision in the placement of the injector sockets in the supply tube because the spacing and orientation of the sockets along the fuel rail assembly must exactly match the three-dimensional spacing and orientation of the fuel injectors as installed in cylinder ports in the engine. Further, a DIG fuel rail must sustain much higher fuel pressures than a MPFI fuel rail to assure proper injection of fuel into a cylinder having a compressed charge. DIG fuel rails may be pressurized to 100 atmospheres or more, for example, whereas MPFI fuel rails must sustain pressures of only about 4 atmospheres.
Efforts to form satisfactory DIG fuel rails by metal forming and welding have not heretofore been successful. The bending and welding processes can produce significant stresses in the formed parts, and even slight misalignments of components such as sockets mounted into the distribution tube can create even further stresses when the assembly is bolted to an engine head.
In response to these problems and requirements, DIG fuel rails typically are formed by precision casting followed by boring of various passages, or by precision/high cost machining of stainless steel. However, prior art cast fuel rails suffer from at least three serious shortcomings. First, they are expensive to manufacture, requiring multiple steps in casting, boring, and finishing. Second, they are typically an aluminum alloy, which is known to be subject to attack by some fuels. Desirable resistant alloys such as stainless steel are more costly to cast. Third, bolts securing a typical prior art fuel rail assembly to an engine head are typically offset from the centerlines of the fuel injectors, such that cylinder pressure on the fuel injectors exerts a torque on the bolts and the assembly which can result in progressive misalignment of the fuel rail with the injectors and potentially failure of the fuel injection system.
What is needed in the art is an inexpensive fuel rail for DIG engine fuel systems.
What is further needed in the art is a DIG fuel rail assembly formed of a non-reactive metal alloy such as stainless steel.
What is further needed in the art is a DIG fuel rail wherein the bolts securing the rail assembly to an engine head lie on the centerline of the fuel injectors.
It is a principal object of the present invention to provide an inexpensive, high-precision fuel rail assembly for use with a DIG or DID internal combustion engine.